Japanese Patent Application (OPI) No. 23538/79 (the term "OPI" as used herein means an "unexamined published application) discloses use of a positive charging toner comprising positive charging Al.sub.2 O.sub.3 and a negative charging core material. Japanese Patent Application (OPI) No. 92545/81 disclosed use of a positive charging toner and non-charging carrier particles.
However, the first such developer system has the disadvantage that a so-called toner cloud phenomenon occurs during use in a developing machine and causes troubles in the copying machine system. On the other hand, the second such developer system has the disadvantage that toner fog occurs on non-image areas of the copy. Further, external addition of hydrophobic silica to a positive charging toner tends to cause charging of an additional toner to the opposite polarity.